Disc conveyor flame ionization detectors

ABSTRACT

Effluent to be tested is deposited on a porous alumina disc, the disc being rotated into a heater where the eluent is vaporized leaving a residue (the sample) whereupon the sample is then transported by the conveyor into a dual jet flame ionization detector (FID). After passing through the FID the disc then passes through an oxidizer where any remaining residue from the disc are removed by oxidation whereupon the disc then passes through a cooler, cooling the disc prior to the disc returning to a point where more effluent will be deposited for further analysis.

@t [19] [1 1] 3,7,479 Szakasits [45] `Baum. 29, H974 [54] DISC CUNVEYORFLAME HONHZATHON 3,527,350 9/1970 Tuthm et ai. 21o/19s C DETECTORSJulius J. Szakasits, Deer Park, Tex. Assignee: Shell Oil Company,Houston, Tex.

Filed: Apr. 13, 1972 Appl. No.: 243,729

Inventor:

U.S. Cl 210/198 C, 73/23.1, 210/179 Int. Cl BOld 15/08 Field of Search55/67, 197, 386, 389, 76;

ZIO/3l C, 198 C, 179; 73/23.l

References Cited UNITED STATES PATENTS 4/l968 Owensa etal. 55/67 5/l97lSamuilor et al 55/197 X Primary Examiner-.lohn Adee Attorney, Agent, orFirm-Theodore E. Bieber et al.

[5 7 ABSTRACT s Claims, 4 Drawing Figures DISC CONVEYOR FLAME IONIZATIONDETECTOIRS BACKGROUND OF THE INVENTION The present invention relates tochromatographic devices and more particularly to a chromatographicdevice using an alumina disc as a sample carrier. The

DESCRIPTION OF THE PRIOR ART- By and large with commercially designeddetectors either the total effluent or a portion of it is deposited on aconveyor of some type. The eluent is then flash evaporated in a heaterleaving a sample material on the conveyor. One methodofdetectioninvolves burning the sample material directly in the flame as theconveyor passes through the detector. An alternate and most frequentlyused concept removes the sample material by pyrolysis in a purgedenclosure from which the pyrolysis products are swept into a FID. Thistechnique is widely used in commercial detectors because it is easier toachieve a better signal to noise ratio than is possible with the directburning technique. Nevertheless sample diffusion on hot metal conveyorswhich manifest itself in the form of signal spikes is still present withmany of the pyrolysisdesigns. The noise problem is more evident with alldesigns when broad peaks are observed, as frequently encountered ingradient elution fractionation and gel permeation chromatography. A U.S.Pat. No. 3,316,674 issued to Owens et al. illustrates using a perforatemetal support such as a platinum screen for a conveyor. When using ametallic or glass surface, the sample deposited by the applicator creepsas the conveyor enters the flame ionization detector which results inback-mixing and noisy peaks in the readout. Another disadvantage inusing a metallic strip as a conveyor is that it distorts due to the heatadded during detection of the sample causing the sample to creep evenfurther than when deposited by the applicator on the metal conveyor.

It has been the practicein the past for the applicator to be made from ametal or glass tube preventing a uniform deposit of all of the effluentson the conveyor without back diffusion or wetting along the externalsurface of the applicator tubing (capillary action). This behaviorcauses both loss and back-mixing. Sample loss occurs when the carriersolvent vaporizes to deposit the sample material in the form of rings 3to 5mm above the tip. The extent of this wetting will vary at constantflow rate and is manifested by a slow pulsation along the applicatortube. As a result, a portion or all of the sample material deposited byone pulse can be diluted subsequently by a more extensive pulse whichdissolves and carries it down to the applicator tip, while placing a newsample ring at a higher position. After analysis, a ring at maximumwetting level is observed on glass and stainless steel applicators.Therefore, the use of such applicators as shown by the prior art devicescauses a substantial variation in the analysis results,

Prior art devices also do not reveal how to ensure against residuebuild-up on the conveyor as a result of the vaporization process leavinga residue on the conveyor resulting in eventual plugging of the pores ofwhatever conveyor type is used. This is not a problem with normalsamples, however, when samples like pitch are analyzed, a non-detectablecarbonaceous residue is left on the conveyor which can result ineventual plugging of the pores causing sample creep, back-mixing andnoisy peaks in the readout equipment.

An even further problem with the prior art devices is that cooling ofthe conveyor is not accomplished other than by normal room air currents.If the disc conveyor is not adequately cooled this results in loss ofsensitivity for lower boiling eluents such as pentane, and increasedbase line instability or noise.

Prior art devices also corporate a single nozzle for the flameionization detector whereas if dual nozzles are used, uniform coverageis accomplished eliminating sample blowout which is caused when only oneflame is used causing further loss of instrument sensitivity andmeaningful analysis results.

SUMMARY OF THE INVENTION The present invention solves the above problemsby incorporating a disc conveyor preferably formed of alumina and havinga high apparent porosity approximating 40 percent which provides anexcellent conveyor for the sample as it is eluted from the applicator.An even further advantage'of the alumina disc conveyor is itsdimensional stability under the application of the heat in the heater,FID and oxidizer assemblies.

A second significant advantage of the present invention is through theuse of an applicator in which a metal tip having apolytetrafluoroethylene (trademark for Teflon) covered outer surface. Byso doing, the present invention has eliminated both sample loss andbackmixing problems as described hereinabove.

A third advantage ofthe present invention is in the use of a dual nozzleflame ionization detector resulting in uniform heating of the discconveyor yielding higher response and eliminating sample blowout.

A further advantage of the present invention is through theincorporation of an oxidizer downstream of the flame ionizationdetector. By use of an oxidizer, the conveyor is burned clean of anyresidues left after passing through the detection device preventingresidue build-up.

An even further advantage of the present invention is incorporation of acooler which surrounds the edge of the disc conveyor. Use of the coolerextends the range of the detector to lower boiling point eluents such aspentane greatly increasing sensitivity and base line stability. I

DESCRIPTION OF THE DRAWINGS The present invention will be more easilyunderstood from the following detailed description of a preferredembodiment when taken in conjunction with the attached drawings inwhich:

FIG. l is a pictorial view of the apparatus constructed according tothis invention;

FIG. 2 is an exploded view illustrating the flame ionization detectorand oxidizer according to the present invention;

FIG. 3 is a cross-sectional view of the disc conveyor; and

FIG. 4 illustrates the stable base line and descriptive peaks obtainedwhen using the apparatus of the present invention.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to FIG. l, there isshown the apparatus constructed accordingto the invention andparticularly adopted for quantitative measurements of eluents from aliquid chromatograph. More particularly, there is shown a control panel30 in which a preferred embodiment of the present invention is mountedcomprising essentially the disc conveyor 29, the applicator 27, theeluent heater and exhaust assembly 25, the flame ionization detector andoxidizer assembly 50, and the dise cooler assembly 31.

An ideal applicator uniformly deposits all of the effluent on theconveyor 29 without back diffusion or wetting along the external surfaceof the applicator wall. Stainless steel and glass tubing have a highlevel of external wetting causing sample loss and backmixing. Toeliminate sample loss and back-mixing the applicator 27 is made from ateflon covered stainless steel syringe needle resulting in excellenteluent deposition and width control for deposition of the sample on theconveyor 29.

The disc conveyor 29 is preferably made of alumina because of itsexcellent dimensional stability in the presence of heat as well as itsuniform porosity distribution. The use of an alumina disc as theconveyor solves many of the problems inherent in prior art devices usingmetallic as well as glass as conveyors, namely, di mensional stabilityand sample containment after being deposited on the conveyor. Thegeneral shape of the disc conveyor 29 is shown in FIG. 3 and is shown ashaving a central bore 58 therethrough with a flat lower surface. Theouter flat surface 51 of the conveyor 29 carries the eluted sample asdeposited by the applicator 27. Optional holes 52 may also be providedin the disc conveyor 29 further lowering the thermal inertia of theconveyor 29. The disc conveyor is mounted on a shaft 48 and retained onthe shaft 48 by a keeper 49. The shaft 48 forms part of a variable speedreversible D.C. motor 49 mountedon the back of control panel 30. Theincorporation of a reversible variable speed motor allows a stable baseline to vbe established by reversing direction of rotation of theconveyor 29 through the oxidizer burning any residue left on conveyor29. In operation, as the disc conveyor rotates clockwise at constantspeed an eluent from a chromatographic column is deposited on theconveyor 29 by the applicator 27. The position of the applicator 27relative to the conveyor 29 is controlled by two micrometer typeadjustments 28 and 28a, one being adapted to position the applicator 27over the conveyor and the other serving to control the distance betweenthe applicator and the surface 51 of the conveyor 29.

Once the sample has been deposited on the conveyor 29 it next passesinto the eluent heater and exhaust assembly 25 where the eluent is flashevaporated leaving the sample on the conveyor 29. The heater and exhaustassembly covers approximately 25 percent of the circumference of thedisc conveyor 29 and is supported by an exhaust duct 60 which is in turnconnected to the heater exhaust blower 10. The blower pulls room airover the conveyor 29 and through duct 60 giving a definite exhaustpattern eliminating hydrocarbons from diffusing into the detector. Theheating element 56 is a screw-plug type element with power regulationfurnished by a silicon-controlled rectifier (SCR) with the temperaturebeing controlled up to 250 C.

Subsequent to being flash evaporated in the heater and exhaust assembly25 the sample to be analyzed next passes through the flame ionizationdetector (FID) and oxidizer assembly 50. The assembly 50 as positionedrelative to the disc conveyor 29 by a second set of micrometeradjustments 13 and 14 providing both horizontal and vertical adjustmentcapability.

The FID and oxidizer assembly 50 is made up of a housing whichpreferably has two chambers 42 and 43. The FID chamber 42 is providedwith bores 72 and 73 for receiving bushings 40 having an eccentric bore75 therethrough. Prior to installing bushings 40 into bores 72, 73 anFID nozzle 22 is inserted through bore 75 of bushing 40 and locked inplace with set screw 41. Subsequently, the bushing 40 with nozzle 22 isinstalled in bores 72, 73 and positioned approximately 2-l0mm from theedge of the conveyor 29 prior to locking the bushing 40 in place by asecond set screw 36 installed in housing 70.

A collector 37 is also positioned within the FID chamber 42. Thecollector 37 consists of semi-circular rings approximately 1.8 cm indiameter spaced 3mm apart and positioned approximately 2mm ahead the FIDnozzles 22. The collector 37 is positioned in the FID chamber 42 using abushing 38 through which an insulator 39 passes. A set screw 37installed in housing 70 contacting bushing 38 allows the finaladjustment of collector 37 relative to the FID nozzles 22 and conveyor29. A view port 23 is provided in the housing 70 to aid in positioningthe detector relative to thc conveyor 29.

As hereinbefore described the FID nozzles 22 are grounded to the housing70. The collector 37 is insulated from the housing 70 by insulator 39.The collector lead wire is connected in series with a 300 volt battery(not shown) which in turn is connected in series with an electrometerthus maintaining a positive collector with respect to the FID nozzles22. Both the collector 37 and FID nozzles 22 are fabricated fromplatinum resulting in very low thermonic noise emission (approximatelyl016 amp/cm2 at l,200 C).

The oxidizer chamber 43 is immediately above the FID chamber 42 andseparatedfrom it by a partitioning element 90. Two oxidizer nozzles 24are inserted through perforations 91 in the housing 70 and each islocked in place by a set screw 36 installed in housing 70. The oxidizerchamber 43 is provided with two vent holes 92 allowing venting of excessheat from the chamber 43. By providing an oxidizer chamber a cleanconveyor is assured by the burning of any residues left on the conveyorafter passing through an FID chamber making the apparatus more versatileand reliable.

An end plate 71 (FIG. 2) encloses the housing 70 opposite the conveyor29. The end plate 71 is provided with an upper cavity 102 with ashoulder 104 against which a sintered stainless steel disc 106 abuts. Alower cavity 103 with a shoulder 105 and sintered stainless steel disc107 are disposed in the lower portion of end plate 71. A plurality ofscrews 111 mate end plate 71 with the housing 70. Air is supplied to theupper cavity 102 by an air inlet fitting 33 threadably inserted in atapped hole 100. Likewise, air is supplied to the lower cavity 103through an air inlet fitting 2l threaded in a tapped hole 101. Bysupplying pressurized air to cavities 102 and 103 covered with sinteredstainless steel disc, air is supplied at a low velocity such thatlaminar flow exists insuring a steady flame in both the FID and oxidizerchamber. By providing this laminar flow the present invention overcomesa further disadvantage of prior art apparatus (point source type airinlet).

Referring again to FIG. 1, a plurality of splitter valves having oneinlet and two outlets are shown. These valves are utilized to facilitatedetector (FID) and oxidizer split ratio for hydrogen and air. Teflontubes interconnect the various fittings for the supply of air andhydrogen in appropriate volumes. Tube 115 connects fitting 17 to fitting33 thereby supplying air to the oxidizer chamber. Tube 116 connects 18to 21 supplying air to the FID chamber. Tube 117 likewise interconnectsfitting 20 to one of the two FID nozzles 22 to supply hydrogen to theFID chamber. Similarly, tube 118 interconnects 20a to the second nozzle22. Finally, tubes 119 and 120 interconnect fittings 19, 19a withoxidizer nozzles 24 supplying hydrogen to the oxidizer chamber 43.

An enclosure 16 having a hingably mounted cover completely encloses theFID and oxidizer assembly and the fittings hereinbefore described. Theenclosure is continuously purged with nitrogen supplied through f1ttingmounted in the control panel 31). By enclosing the FID and oxidizer,background noise produced from room air currents is eliminated furtherincreasing instrument sensitivity and reliability.

A further advantage of the present invention is through theincorporation of a disc cooler assembly 31 which greatly extends therange of the instrument to lower boiling point eluents such as pentane.The assen bly 3l is mounted on the control panel 30 having an opening124 in communication with a duct 125. A cooler exhaust blower 34 drawslarge volumes of room air over the conveyor 29 exhausting room air isindicated by the arrows 35. Alternately, if the room air temperature ishigher than desired a fitting 130 is provided in the disc coolerassembly 31 whereby nitrogen can be supplied aiding in cooling of theconveyor 29. The disc cooler eliminates residual heat in the conveyorand prevents vaporizing of the eluent upon contact when deposited by theapplicator 27 on conveyor 29. Premature vaporizing will partially orcompletely carry the sample material away with the vaporized eluentdestroying any meaningful results of the analysis. The use of a coolerfurther increases sensitivity and base line stability of the instrument.

I claim:

1. A chromatographic device comprising:

a circular disc conveyor mounted for rotation about a central axis;

means for rotating said conveyor at substantially constant speed aboutsaid central axis;

an applicator, said applicator being positioned adjacent the path ofsaid disc to deposit eluents from a liquid chromatographic column nearthe outer edge of said conveyor;

a heater, said heater being disposed adjacent the path of the outer edgeof said conveyor, spaced from said applicator in the direction ofrotation of said conveyor and adapted to flash evaporate eluent carriedby said conveyor;

a flame ionization detector, said detector being disposed adjacent thepath of the outer edge of said conveyor to direct its flame onto saidconveyor;

an oxidizer, said oxidizer being disposed adjacent the path of the outeredge of said conveyor and adapted to burn impurities carried by saidconveyor after said conveyor passes through said flame ionizationdetector; and

a cooler, said cooler being disposed adjacent the path of the outer edgeof said conveyor adapted to cool said conveyor subsequent to saidconveyor passing through said oxidizer.

2. The apparatus of claim 1 wherein said circular disc conveyor is ofalumina.

3. The apparatus of claim 1 wherein said applicator is a Teflon coveredstainless steel syringe needle.

4l. The apparatus of claim 1 further including an enclosuresubstantially enclosing said flame ionization detector and oxidizer,said enclosure being continuously purged with nitrogen.

5. The apparatus of claim 1 further including an exhaust and coolerblower for exhausting from said heater and said cooler, said blowersbeing in fluid communication with said heater and said cooler.

6. A chromatographic device comprising:

a circular disc, said disc being rotatably mounted on its central axis;

a drive means coupled to said disc for rotating said disc at asubstantially constant speed;

an applicator, said applicator being mounted to deposit the eluents froma liquid chromatographic column on the flat surface of the disc adjacentthe outer periphery thereof;

a heater, said heater having a passageway with a U- shaped cross-sectionand mounted with the legs of said passageway extending along thesurfaces of said disc adjacent the periphery thereof;

a flame ionization detector, said flame ionization detector having apassageway with a U-shaped crosssection and mounted with the legsextending along the surfaces of said disc adjacent the outer peripherythereof;

an oxidizer, said oxidizer having passageway with a U-shapedcross-section and mounted with the legs extending along the surfaces ofthe disc adjacent the periphery thereof; and

a cooler, said cooler being disposed to cool both sides of said discadjacent the outer periphery thereof.

7. The chromatographic device of claim 6 wherein the passageway inv saidheater has sufficient length to cover substantially twenty-five percentof the periphery of said disc.

8. The chromatographic device of claim 6 wherein said flame ionizationdetector utilizes a pair of nozzles to direct a flame onto both sides ofsaid disc.

l =l =l l 2k

1. A chromatographic device comprising: a circular disc conveyor mountedfor rotation about a central axis; means for rotating said conveyor atsubstantially constant speed about said central axis; an applicator,said applicator being positioned adjacent the path of said disc todeposit eluents from a liquid chromatographic column near the outer edgeof said conveyor; a heater, said heater being disposed adjacent the pathof the outer edge of said conveyor, spaced from said applicator in thedirection of rotation of said conveyor and adapted to flash evaporateeluent carried by said conveyor; a flame ionization detector, saiddetector being disposed adjacent the path of the outer edge of saidconveyor to direct its flame onto said conveyor; an oxidizer, saidoxidizer being disposed adjacent the path of the outer edge of saidconveyor and adapted to burn impurities carried by said conveyor aftersaid conveyor passes through said flame ionization detector; and acooler, said cooler being disposed adjacent the path of the outer edgeof said conveyor adapted to cool said conveyor subsequent to saidconveyor passing through said oxidizer.
 2. The apparatus of claim 1wherein said circular disc conveyor is of alumina.
 3. The apparatus ofclaim 1 wherein said applicator is a Teflon covered stainless steelsyringe needle.
 4. The apparatus of claim 1 further including anenclosure substantially enclosing said flame ionization detector andoxidizer, said enclosure being continuously purged with nitrogen.
 5. Theapparatus of claim 1 further including an exhaust and cooler blower forexhausting from said heater and said cooler, said blowers being in fluidcommunication with said heater and said cooler.
 6. A chromatographicdevice comprising: a circular disc, said disc being rotatably mounted onits central axis; a drive means coupled to said disc for rotating saiddisc at a substantially constant speed; an applicator, said applicatorbeing mounted to deposit the eluents from a liquid chromatographiccolumn on the flat surface of the disc adjacent the outer peripherythereof; a heater, said heater having a passageway with a U-shapedcross-section and mounted with the legs of said passageway extendingalong the surfaces of said disc adjacent the periphery thereof; a flameionization detector, said flame ionization detector having a passagewaywith a U-shaped cross-section and mounted with the legs extending alongthe surfaces of said disc adjacent the outer periphery thereof; anoxidizer, said oxidizer having passageway with a U-shaped cross-sectionand mounted with the legs extending along the surfaces of the discadjacent the periphery thereof; and a cooler, said cooler being disposedto cool both sides of said disc adjacent the outer periphery thereof. 7.The chromatographic device of claim 6 wherein the passageway in saidheater has sufficient length to cover substantially twenty-five percentof the periphery of said disc.
 8. The chromatographic device of claim 6wherein said flame ionization detector utilizes a pair of nozzles todirect a flame onto both sides of said disc.